Run: Nadal is on course to win his fifth Masters 1000 title of the season

Edge: Berdych (below) has not beaten the Spaniard since 2006

The Czech came out swinging in the second set and his aggressive approach paid dividends when he broke for a 4-2 lead. But he surrendered the advantage immediately and the set went to a tie-break, which Nadal edged to seal his progress.

Nadal, who is closing in on world No 2 Andy Murray in the rankings, was delighted with his performance.

He told atpworldtour.com: 'I think I played a very good match this afternoon against a very difficult opponent who came to this match playing very well, and I have to be very, very happy about everything.'

Nadal will next face Isner - a boost for American tennis, which reached a historic low on Monday when the big-server dropped out of the top 20, making it the first time since the rankings began that no US player has been at that level.

Roar: John Isner will play Nadal in the final after beating Juan Martin Del Potro

Back from the brink: The American came from a set down to beat Del Potro in Cincinnati

Scalp: Isner beat world No 1 Novak Djokovic earlier this week en route to the final

But the 28-year-old has answered the critics in the best possible fashion with one of the best weeks of his career.A day after stunning world No 1 Djokovic in the quarter-finals, he recovered from a seemingly impossible position to beat seventh seed Del Potro.

Del Potro broke to lead 5-3 in the second set and held a match point but served a double fault, Isner broke back and then took his fifth chance in the tie-break.

The Argentine looked lethargic and could find no way back after Isner won the first three games of the decider.

Isner told Sky Sports: 'As of right now I'm just very thrilled to be in the final. I've got to get myself ready and I know it's going to be another tough match. I certainly believe I can beat anyone, and if I can take that belief onto the court tomorrow I'm going to give myself a shot.'

The women's final will be between the top two seeds, Serena Williams and Victoria Azarenka, who both battled to victories in their semi-finals.

Showdown: Serena Williams will play Victoria Azarenka (below) in the women's final

Williams came out on top in a topsy-turvy encounter with defending champion Li Na, eventually sealing a 7-5 7-5 win. Li won four straight games to lead 5-4 in the first but double-faulted at set point to let Williams back in.

The fifth seed served the second set as well, having been a break down, but again Williams got the break back and went on to seal the match.

Williams told wtatennis.com: 'Whenever I'm down I just get really relaxed. I was just thinking, "You know Serena, just try to do your best, and just try to do what you can".'

Azarenka meanwhile came from a set down to beat Jelena Jankovic 4-6 6-2 6-3. Azarenka has only beaten Williams twice in 14 attempts, although one of those was earlier this year on a hardcourt in Doha.